The present invention relates to night vision systems. More particularly, the present invention is related to an active night vision system with adaptive imaging.
Night vision systems allow a vehicle occupant to better see objects during relatively low visible light level conditions, such as at nighttime. Night vision systems typically are classified as either passive night vision systems or active night vision systems. Passive systems simply detect ambient infrared light emitted from the objects within a particular environment. Active systems utilize a near infrared (NIR) light source to illuminate a target area and subsequently detect the NIR light reflected off objects within that area.
Passive systems typically use far-infrared cameras that are characterized by low resolution and relatively low contrast. Such cameras must be located on the vehicle exterior in order to acquire requisite infrared energy in the operating environment. Externally mounted cameras can negatively affect vehicle styling. Far-infrared cameras are also costly to manufacture and generate non-intuitive images that can be difficult to interpret.
Active systems provide improved resolution and image clarity over passive systems. Active systems utilize laser or incandescent light sources to generate an illumination beam in the near infrared spectral region and charge-coupled devices or CMOS cameras to detect the reflected NIR light.
Diode lasers are preferred over incandescent light sources for several reasons. Incandescent light sources are not monochromatic like diode lasers, but instead emit energy across a large spectrum, which must be filtered to prevent glare onto oncoming vehicles. Filtering a significant portion of the energy generated from a bulb is expensive, energy inefficient, and generates undesired heat. Also, filter positioning is limited in incandescent applications, since the filter must be located proximate an associated light source. As well, multiple incandescent sources are often required to provide requisite illumination, thus increasing complexity and costs.
In an exemplary active night vision system a NIR laser is used to illuminate a target area. A camera is used in conjunction with the laser to receive reflected NIR light from objects within the target area. The laser may be pulsed with a duty cycle of approximately 25–30%. The camera may be operated in synchronization with the laser to capture an image while the laser is in an “ON” state.
The camera typically contains a band-pass filter that allows passage of light that is within a narrow range or band, which includes the wavelength of the light generated by the laser. The combination of the duty cycle and the use of the band-pass filter effectively eliminates the blinding effects associated with headlamps of oncoming vehicles. The term “blinding effects” refers to when pixel intensities are high due to the brightness of the oncoming lights, which causes an image to be “flooded out” or have large bright spots such that the image is unclear.
Most active night vision systems employ a fixed field of view presented to the vehicle operator. If the field of view is set too wide, it makes identifying distant objects difficult, particularly at high speeds. If it is set too narrow, it can lack appropriate coverage at low vehicle speeds or while turning the vehicle. Thus, most variable field of view display systems employ a mechanical zoom control on the camera lens, or a mechanical steering mechanism to point the system in the region of interest. Such mechanical controls, however, increase system complexity and, resultantly, system cost and potential warranty claims.
Thus, there exists a need for an improved active night vision system and method of generating images that provides an adaptive field of view related to vehicle speed or direction.